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iPhone accelerometer.

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Simon Spooner, Oct 14, 2010.

  1. Re: i-phone accelerometer.

    I got this app: http://www.dld-llc.com/Diffraction_Limited_Design_LLC/Vibration.html

    This is ace (Dave Smith, if you got an i-phone, you got to get this!)

    "The frequency data can be converted to velocity (touch integrate once) or displacement ( touch integrate again). The values reported are in mm/sec (in/sec) for velocity and mm (in) for displacement."

    Just a shame you can't put it under your foot, but you can strap it your leg etc....I got projects coming out of my ears. And all for a couple of quid. Brilliant!!!!!!!!!!!!!!!!
  2. Craig Payne

    Craig Payne Moderator

  3. Re: i-phone accelerometer.

    Craig, this does so much more. I think you'll find an application or twelve for it, it's a 3D force gauge.
  4. Re: i-phone accelerometer.

    Tibial acceleration during treadmill walking.... captured on my i-phone.

    Attached Files:

  5. Re: i-phone accelerometer.

    I just got this:

    These apps appear to give potential for highly sophisticated movement analyses. The key is going to be in attaching the iphone to the segment of choice and to minimise movement error between the phone and the body segment, I thought about super-glue, but perhaps not.... any ideas?
  6. Griff

    Griff Moderator

    Re: i-phone accelerometer.

    My mrs uses a neoprene cuff around her arm when she uses her iphone for running etc. Would something like that do the trick? The phone doesn't move at all in the cuff. Might have potential source of error with the cuff moving relative to the body segment though?
  7. Re: i-phone accelerometer.

    Got one on my desk at work.... haven't had chance to try it yet, need to take the case off my phone to fit it in... Can't get it tight enough to fit around the distal leg though.. I might need to modify it... It may be a gaffer tape job though.
  8. CraigT

    CraigT Well-Known Member

    Re: i-phone accelerometer.

    Thanks for highlighting this Simon!
    Do you have a iPhone 4?
    Another option is using a iPod touch- the latest generation also has the gyroscope of the iPhone 4, and is lighter (and cheaper)
  9. Re: i-phone accelerometer.

    I'm an i-phone 4 man, myself. I can't believe how cool this is. It's just a shame that the i-phone isn't about a quarter of the size it is. never the less, I'm going to collect some data and see what we can see. Between day error first.
  10. Ian Drakard

    Ian Drakard Active Member

    Re: i-phone accelerometer.

    Ouch! I guess we'll know when you've tried it by the sound of gaffer tape leg wax induced screaming ;)
  11. Re: i-phone accelerometer.

    Toughen up, please.;) It's not quite the same as that which one of my heroes put himself through: http://en.wikipedia.org/wiki/John_P._Stapp

  12. Re: i-phone accelerometer.

    Just collected acceleration data using the vibration app. I-phone attached to distal tibia. Running shod (Nike Zoom Elite) versus barefoot treadmill running, running speed constant between trials. Sample frequency 50HZ , acquisition time 17.96 seconds. Here's the results:

    RMS (root mean square) X =+ 0.721g
    RMS Y = + 0.598g
    RMS Z = +0.868g

    RMS = +1.277g

    RMS X= + 0.902
    RMS Y= + 0.686
    RMS Z= +0.865

    RMS= +1.426g

    3d axes of I-phone here:
  13. David Smith

    David Smith Well-Known Member

    Re: i-phone accelerometer.


    Hey that's really cool eh! Makes you wonder about the reliability of the data when pro accelerometer sets with software cost 100's to thousands. However making comparatives between 'normal' and pathological gate might be useful.

  14. David Smith

    David Smith Well-Known Member

  15. David Smith

    David Smith Well-Known Member

    Re: i-phone accelerometer.


    Looks impressive. Doesn't say if/how the signal raw data is processed, like is it smoothed, filtered, windowed, and is/can biasing be removed. I don't know what a hamming window is do you? OK now I do - go here -


    Its a type of filtering window

    Even cooler, it would be handy if you could also import external data and process and analyse it.

    Regards Dave
  16. Re: i-phone accelerometer.

    Dave, there is also a users forum where you can ask technical questions/ make suggestions:

    Although I actually think this app is better: http://www.wavefrontlabs.com/Wavefront_Labs/Sensor_Data.html
    You have to import the data into a spreadsheet programme, e.g. excel to create charts and analyse; also their is no capacity to trigger data capture- but again the developers are open to suggestions.

    I've also been looking at some video motion analysis apps... this is free:
  17. Re: i-phone accelerometer.

    Been playing with this on my old Iphone (no gyro). Accel graph is a nice app, easy to use.

    Simon, name your segment, I'll make you something to hold the phone to it. Software and electronics I'm not so hot. Hardware and such, I can do. Thin layer of Gel to adhere to the skin, moulded EVA to hold it vertical. Simples.
  18. Re: i-phone accelerometer.

    Distal tibia would seem a good starting point.
  19. Re: i-phone accelerometer.

    I'll get right on that. Shouldn't be beyond the wit of man.
  20. Re: i-phone accelerometer.

    Cheers Robeer. Remember my iphone is bigger than yours.;) No it really is, the iphone 4 is bigger than the 3G
  21. Re: i-phone accelerometer.

    Duly Noted. ;) You got a suit of armour on it as well. I'll take that into account too.

    I have Gyro envy. :eek:
  22. Re: i-phone accelerometer.

    Suit of armour is removable. I got a cheap plastic case that the iphone will clip into, I was going to use this with some gel/ carpet tape on the back and a couple of straps, but if you can create something better......
  23. Re: i-phone accelerometer.

    Do bruins deficate in rural forested areas?
  24. Re: i-phone accelerometer.


    Which ever gives the lowest between day variation is the winner.
  25. Re: i-phone accelerometer.

    p.S. don't forget I need two: one for each leg, I've just procured a dummy iphone 4 to strap to the other leg to keep things balanced.
  26. Re: i-phone accelerometer.

    Been mulling / playing. Hit a snag.

    The easiest and most secure way to simply attatch it is with a strip of theraband. However if the phone is not flat to the frontal plane, will it not cause a paralax error? For eg, my phone has the x axis pointing down the short side. If the device is in the frontal plane, this will not change during extension / flexion. However if the device is at 45 degrees then we see x change.

    And if I Do hold it to the frontal plane (and I have a prototype which does this) what of the rotation of the leg? If I was trying to get sagittal plane data, the frontal plane rotation changes my readings!

    Also, what postion do I place the leg in when aligning the device to the frontal plane. RSCP? NSCP? Based on the tibial tuberoscity?

    I Wondered if one can manually calibrate the data. Ie, have the patient stand still for 10 seconds before walking and deduct the XYand Z value from the dynamic data (simulating a baseline).

    Hmmm. Bit tricky this. I've made 3 rigs, all of which hold the device securely in place with little or no movement, but I don't know WHERE i am trying to hold it and relative to what. Or am I trying to calibrate my own base position?

    Had another idea though. Strap the phone to the sole of the foot and use it to examine sub talar range and axis of motion (use a low pass filter). Thats crazy fun. Wonder if you could build a shoe with a segment in the sole for the phone.
  27. Re: i-phone accelerometer.

    Get an iphone 4 with a gyroscope so you know the rotations!
    Might be worth checking the literature to see how this has been approached previously. Google: tibial acceleration

  28. Re: i-phone accelerometer.

    Hark At Rockerfella!

    Well in that case you don't really need rigzilla


    You're probably best off just using a strip of theraband! Holds it very firmly.

  29. Re: i-phone accelerometer.

    The trouble with rigzilla is the accelerometer needs to be attached rigidly to the tibia (i.e a bone pin would be gold standard), by having a big block of foam there it will dampen the vibrations.

    Nobody seems too worried about the rotation of the accelerometer axes relative to the global co-ordinate systems in the published research I've read which has employed triaxial accelerometers... Perhaps someone more knowledgeable will comment.
  30. Re: i-phone accelerometer.

    Yeah, I think your right. Its eva so its pretty tough, but still.

    In that case, Theraband is perfect. very snug,
  31. Karen Knightly

    Karen Knightly Active Member

    Re: i-phone accelerometer.


    I have an iphone 4, where's the gyroscope, does it come with it or is it a separate app?

  32. Re: i-phone accelerometer.

    hi Karen, the gyroscope is within your phone, to access data from it you need the app "sensor data" from wavefront labs. I linked to it earlier in this thread.
  33. Karen Knightly

    Karen Knightly Active Member

    Re: i-phone accelerometer.

    Thanks Simon, sorry, I missed your ref to the link earlier!
  34. Re: i-phone accelerometer.

    No worries Karen. Are you just curious or are you planning to do some study with this technology? If so, I'd love to get involved.
  35. Karen Knightly

    Karen Knightly Active Member

    Re: i-phone accelerometer.

    Simon, at this stage I am just curious, but that's not to say I wouldn't like to get involved at a later stage. I'm very interested in the possibilities emerging with using both the iphone and ipad's apps
  36. stew90

    stew90 Welcome New Poster

    I have not been able to read all the links that have been posted in this thread, but the idea of using data from this app for walking or running at 50 Hz really should be met with caution....with ground contact in running being only 0.2-0.3 seconds...this is only 12.5 data points, and to look at tibia acceleration when it will be at its highest will probably only involve 2-3 of these data points...to then start using this for velocity or displacement data will just not give usable informaion.

    As a tool strapped to the back to measure overall body COM during jumping or walking possibly...but tibia accelerations at heel strike need a much higher recording speed...hence commercial products recording in the hundreds or thousands Hz ranges.
  37. COM displacement now thats something - we know from research earlier this yes that the COM is around the belly button -

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